The present invention relates to an automatic transmission, and more particularly, to a method and system for determining a fill time for friction elements of an automatic transmission.
In automatic transmissions used for vehicles, a shift control system controls the automatic shifting between different speeds and shift ranges according to various factors including throttle opening, vehicle speed, and load, and various engine and driving conditions detected through a plurality of sensors. That is, based on such factors, the shift control system controls a plurality of solenoid valves in a hydraulic control system such that the hydraulic flow controls the shifting of the transmission into the various shift ranges and speeds within the ranges (where applicable).
More specifically, when the driver manipulates a shift lever to a desired shift range, a manual valve of the hydraulic control system undergoes port conversion as a result of the manual valve being indexed with the shift lever. By this operation, hydraulic pressure generated by a hydraulic pump (i.e., the hydraulic pump generates hydraulic flow that results in hydraulic pressure) selectively engages a plurality of operational elements of a gearshift mechanism according to the duty control of the solenoid valves, thereby realizing shifting to the desired shift range.
The automatic transmission operating as above includes friction elements, which, when shifting to the desired shift range, are converted from an engaged to a disengaged state and from a disengaged to an engaged state.
Such friction elements typically include metal bands and/or clutches for controlling the planetary gears in the transmission. The friction elements are actuated by hydraulic pistons and the references to fill time as used herein are to the time for filling/actuating the hydraulic pistons that, in turn, engage the friction elements. After control signals for the supply of hydraulic pressure to the friction elements are input to the solenoid valves, control is performed and hydraulic pressure passes through predetermined lines for supply to the friction elements. The time from the instant the control signals are transmitted to the moment the friction elements are fully engaged is referred to as the fill time. Fill time can also be thought of as the time required for the friction elements to change from a disengaged to an engaged state following the application of a control signal (since the transmission time for the signal can be considered instantaneous).
Since the friction elements must engage at a precise moment, the application of the control signals must precede the time interval needed to engage the friction elements and extend back over the fill time. Hence, the determination of the fill time is a factor in realizing precise control of the automatic transmission.
In the case where automatic shifting is performed between different speeds in the D-range (e.g., first through fourth speeds), established standard fill times for specific friction elements may be called from a memory by a transmission control unit. The timing at which the solenoid valves are driven is determined from the established standard fill times.
There are instances, however, when the select lever is changed many times between the drive range (D-range), neutral range (N-range), and the reverse range (R-range) in a short interval (for example when parallel parking). During such operation, the select lever may be re-positioned before the full engagement or disengagement of the friction elements takes place. Therefore, it becomes necessary for the fill times of the friction elements to be determined in real-time every instance the select lever is manipulated into a different position.
In one prior art method for determining the fill times of the friction elements, modeling of the exhaust and supply of hydraulic pressure during shifting between the D-, N-, and R-ranges is not based on the actual stroke of the pistons driving the friction elements, but rather on linear equations that do not accurately describe the action of the pistons. Accordingly, if shifting is performed during the exhaust or supply of hydraulic pressure, errors result in the determination of the strokes of the pistons that drive the friction elements, which are engaged and disengaged during the shift operation.
As a result of such errors in the determination of the piston stroke ratios, precise fill time values cannot be determined during relatively quick, successive shifting between the D-, N-, and R-ranges. Hence, the friction elements are not driven at precise times such that shift quality varies and shift shock may occur.
The present invention provides a method and system for determining a fill time of friction elements of an automatic transmission, in which, in the case where a select lever is successively operated between a D-range, an N-range, and a R-range over a short interval, a stroke ratio of pistons driving the friction elements is calculated and a fill time of the friction elements is determined based on this calculation.
According to one embodiment of the invention, a friction element of an automatic transmission is either engaged or disengaged during shifting between an N-range, a D-range, and an R-range. The method comprises neutral compensating, in which a piston stroke ratio is compensated by detecting an N-range hold time and using the detected N-range hold time and a pre-installed map when an N to D/R shift signal (indicating shifting into one of the D- and R-ranges from the N-range) is detected; drive compensating, in which a piston stroke ratio is compensated by detecting a D/R-range hold time and using the detected D/R-range hold time and the pre-installed map when a D/R to N shift signal (indicating shifting into the N-range from one of the D- and R-ranges) is detected, the D/R-range hold time being the time during which the shift range is held at said one of the D- and R-ranges; and calculating a fill time using the compensated piston stroke ratio.
According to a preferred embodiment of the present invention, the neutral compensating comprises determining if the N to D/R shift signal is detected; initializing, in the case where the N to D/R shift signal is detected, a timing device after the N-range hold time is detected; calculating a change in an N to D/R piston stroke ratio from the pre-installed map using the N-range hold time; and compensating the piston stroke ratio based on the change in the N to D/R piston stroke ratio.
In another preferred embodiment of the present invention, the piston stroke ratio is compensated by adding the change in the N to D/R piston stroke ratio to the piston stroke ratio.
According to yet another embodiment of the present invention, the drive compensating comprises determining if the D/R to N shift signal is detected; initializing, in the case where the D/R to N shift signal is detected, a timing device after the D/R-range hold time is detected; calculating a change in a D/R to N piston stroke ration from the pre-installed map using the D/R-range hold time; and compensating the piston stroke ratio based on the change in the D/R to N piston stroke ratio. Preferably, the piston stroke ratio is compensated for by adding the change in the D/R to N piston stroke ratio to the piston stroke ratio.
In a further alternative embodiment of the present invention, the method further comprises detecting a compensation start signal of the piston stroke ratio; initializing the piston stroke ratio and a timing device; repeating the neutral compensating, drive compensating, and calculating the fill time until shifting occurs into a shift range other than the R-, N-, and D-ranges. The compensation start signal for the piston stroke ratio is a D/R to N shift signal indicating shifting into the N-range from one of the D-range and the R-range. Initialization of the timing device is such that the timing device is initialized to 0, and initialization of the piston stroke ratio is such that the piston stroke ratio is initialized to 1 in the case of a friction element that is disengaged during shifting into the N-range and to 0 in the case of a friction element that is engaged during shifting into the N-range.
Preferably, the fill time may be calculated using the equation xe2x80x9cfill time=(1xe2x88x92St)*Tbxe2x80x9d, where St is the piston stroke ratio and Tb is a predetermined standard fill time. Moreover, preferably the fill time is calculated based on the piston stroke ratio and using an inverse map of the pre-installed map.
The system for determining a fill time of a friction element of an automatic transmission comprises a shift lever detector for detecting a position of a shift lever, which is operated by a driver, and outputting a corresponding shift lever change signal; a timing device for measuring time intervals between a change in position of the shift lever, and outputting a corresponding time signal; and an electronic control unit for calculating a friction element fill time when the shift lever change signal is input in which the friction element fill time is calculated based on a piston stroke ratio of a piston that drives a friction element. The electronic control unit (ECU) compensates the piston stroke ratio by detecting an N-range hold time and by using the detected N-range hold time and a pre-installed map when an N to D/R shift signal, indicating shifting into one of the D- and R-ranges from the N-range, is detected. The ECU also compensates the piston stroke ratio by detecting a D/R-range hold time and using the detected D/R-range hold time and the pre-installed map when a D/R to N shift signal, indicating shifting into the N-range from one of the D- and R-ranges, is detected. The D/R-range hold time is the time during which the shift range is held at said one of the D- and R-ranges. The ECU then calculates a fill time using the compensated piston stroke ratio.
According to the present invention, when it is determined if the N to D/R shift signal has been detected, the timing device is initialized after the N-range hold time is detected, in the case where the N to D/R shift signal is detected. A change in the N to D/R piston stroke ratio is calculated from the pre-installed map using the N-range hold time and the piston stroke ratio is compensated based on the change in the N to D/R piston stroke ratio. Alternatively, when it is determined if the D/R to N shift signal has been detected, the timing device is initialized after the D/R-range hold time is detected, in the case where the D/R to N shift signal is detected. A change in the D/R to N piston stroke ratio is calculated from the pre-installed map using the D/R-range hold time and the piston stroke ratio is compensated based on the change in the D/R to N piston stroke ratio.
Preferably, the processes of detecting a shift signal, compensating the piston stroke ratio, and calculating the fill time are repeated until shifting occurs into a shift range other than the R-, N-, and D-ranges.
In a further preferred embodiment, the fill time is calculated using the equation xe2x80x9cfill time=(1xe2x88x92St)*Tbxe2x80x9d, where St is the piston stroke ratio and Tb is a predetermined standard fill time. The fill time also may be calculated based on the piston stroke ratio and using an inverse map of the pre-installed map.